Navigational instruments for aircraft which continously provide the position of the aircraft in a UTM grid coordinate system are known. Such navigational instruments may, for example, comprise Doppler radar equipment which continuously measures the ground speed of the aircraft. From this speed, the heading provided by the compass unit, and the flight time, the distance components associated with the flight path covered are computed continously, and the grid coordinates of the aircraft position are continously formed therefrom. The digital position display obtained thereby is not very illustrative and would have to be laid off on a map. This would stress and distract the pilot in an undesirable manner.